Radiation hardening is a method of designing and testing electronic components and systems to make them resistant to damage or malfunctions caused by ionizing radiation (particle radiation and high-energy electromagnetic radiation), such as would be encountered in outer space, high-altitude flight, around nuclear reactors, particle accelerators, during nuclear accidents or nuclear warfare. For example, gamma rays are produced in fission and as a result of other neutron reactions and nuclear excitation of the weapon materials. These rays appear within a second or less after a nuclear explosion. The radiations from these sources are known either as prompt or instantaneous gamma rays. Such radiations cause damage or malfunctions to semiconductor devices.
An integrated circuit with both analog circuits and digital circuits on a single semiconductor die is known as a mixed-signal integrated circuit. In a prompt dose radiation environment mixed-signal integrated circuits are particularly susceptible to functional disruption due to signal level changes induced during the radiation pulse. Various radiation hardening techniques are in use today to harden the mixed-signal integrated circuit.
FIG. 1 illustrates one such common circuit hardening techniques. The radiation hardening apparatus 100 includes an external capacitor 110 added to a plurality of power supply pins 108 in a semiconductor device package 102. This avoids signal level changes in an integrated circuit 104 during prompt dose radiations. An internal analog circuit 106 generates an internal reference voltage that has been used for various purposes in the semiconductor integrated circuit 104. However the external capacitor 110 does not harden the changes in internal reference voltage during prompt dose radiations.
Internally generated analog reference voltages, however, are more difficult to harden because there is a practical limit to the amount of in-circuit capacitance that can be added to the chip without affecting die size. Also an increase in on-chip capacitance typically also decreases defect driven yield and increases susceptibility to heavy ion induced dielectric rupture.
A need, therefore, exists for an improved way to radiation harden circuits having internally generated analog voltages.